JPH04313040A - Method for testing strength of optical fiber - Google Patents

Abstract

PURPOSE: To determine the range of strength for a given length at different tension levels by applying an increasing tension to an optical fiber of indexed length between a clamp point and a tension applying point. CONSTITUTION: A given length of an optical fiber 11 is fed from a supply reel 12 and wound, at least partly, around the tractor wheels 21, 22 of first and second track assemblies 24, 25 perpendicularly to the axis thereof. The fiber 11 is looped around a grooved wheel 19 and a grooved dancer 23 and passed through a tension stud assembly 40. Consequently, movement of the fiber 11 is restricted with respect to the wheels 21, 22 and a tension, increasing from an initial level to a predetermined maximum load, is applied from an assembly 40 to the part of the optical fiber between the wheels 21, 22. An actual breakdown load is held in a memory upon breakage of the optical fiber, otherwise a different part is tested.

Description

[Detailed description of the invention]

0001

FIELD OF THE INVENTION This invention relates to a method for characterizing the lower end of the intensity distribution for many kilometers of optical fiber in a relatively short time.

0002

BACKGROUND OF THE INVENTION Measurement techniques for optical fibers are known. Testing of optical fibers includes: 1) optical properties, including overall attenuation and loss; 2) mechanical parameters, including fiber size and core/cladding dimensions;
and 3) the strength-related properties of optical fibers.

[0003] Usually, the long-term reliability of optical fibers depends on the strength of the glass. The strength of glass is regulated by the presence of cracks and scratches. The occurrence of cracks easily breaks strong glass optical fibers and greatly reduces their strength. Cracks can be generated by chemical or mechanical means. The presence of a crack causes the glass optical fiber to break at a predetermined stress. Therefore, to evaluate the reliability of a glass optical fiber, the glass optical fiber must be strength tested by applying tension to detect cracks and flaws.

Optical fiber manufacturers usually conduct durability tests at their factories. Endurance testing of optical fibers provides data to monitor the manufacturing process and improve the product. However, users will require durability testing of optical fibers to ensure that all wound optical fibers have at least the minimum level of strength necessary for safe handling without breakage. How many kilometers is that level?
There is a considerable probability of testing the full length of the tor5.
Set to a value such as 0 or 100 kpsi.

US Pat. No. 4,148,218 discloses an apparatus for testing the strength of optical fibers. The device applies a preset tension to a continuous length of optical fiber such that a flaw with an intensity less than the preset tension is detected as a break in the optical fiber. First and second tractor assemblies are used to apply a preset tension to the optical fiber. As the optical fiber exits the furnace or exits a reel of previously drawn optical fiber, it is threaded through the first tractor assembly. While the apparatus of the above-mentioned US patent is capable of testing relatively long lengths of optical fiber, it has a major drawback in that it cannot be applied to determine actual failure loads for a range of strengths.

Static fatigue test equipment is conventional. Static fatigue is time dependent in the sense that failure actually occurs when the stress exceeds a certain minimum value. An example of a conventional static fatigue testing device requires loading a certain length of optical fiber with a certain weight. The weight tensions the optical fiber until it breaks after a predetermined time. This type of equipment has a limit to the number of optical fibers that can be tested at a given time. A major problem with this type of testing is that all optical fibers must be tested to failure. Another difficulty is how many kilometers
This means that it is difficult to test the length of torque in a short period of time. It is impractical to test kilometers of optical fiber over many years.

One example of conventional dynamic fatigue testing equipment involves applying increasing tension to individual optical fibers. Apply increasing tension until the optical fiber breaks and record the actual load at break. Some of these test devices are environmentally (temperature and/or humidity) controlled. Both of the test devices described above are time consuming to set up and require loading. For a general description of static and dynamic fatigue test equipment, see Journal of the American Ceramic Society, Vol. 61, No. 11
-12, November-December 1978, No. 518-52
See the article by Kalish and Tariyal, "Static and Dynamic Fatigue of Polymer-Coated Fused Silica Optical Fibers," at page 3.

[0008] The above-described conventional test equipment is particularly significant in that it reflects the inability in the prior art to conceive of a device for continuously testing the strength of optical fibers. Conventional testing equipment cannot measure the strength distribution of only low-strength fractures. Therefore, the first aspect of the present invention
A preferred embodiment thereof provides a method and apparatus that is particularly suitable for automatically testing reels of optical fiber and detecting the actual breaking load of a low-strength break. That's true. The purpose of the invention is to determine the range of actual strength values for a given length of optical fiber at different tension levels and to measure the breaking load without breaking any part of the length of the optical fiber. The purpose is to provide a method.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to determine the range of actual intensity values for a given length of optical fiber at different tension levels and for any part of the length of the optical fiber. It is an object of the present invention to provide a method for measuring failure load without causing failure.

0010

SUMMARY OF THE INVENTION In accordance with the present invention, successively indexed lengths of optical fiber are automatically measured for failure load for each break below a predetermined maximum stress.

In one embodiment of the present invention, a method is provided for testing an optical fiber to detect the breaking load for each break below a predetermined maximum load. A predetermined length of optical fiber is indexed. The optical fiber is clamped at one or more clamp points along its length. An increasing tension is applied to the first indexed length of optical fiber between the at least one clamp point and the tension applying means. An increasing tension is applied between the initial value and the predetermined maximum load. The increasing tension is measured at the time of its application. When failure occurs, the actual failure load is detected while increasing tension is applied. If failure does not occur, the first indexed length of optical fiber is released and the second indexed length of optical fiber is inserted between the at least one clamping point and the tensioning means. Indexed to a position where increasing tension is applied to a second length.

In another embodiment of the invention, an apparatus is provided for testing optical fibers to detect the breaking load for each break below a predetermined maximum load. A first length of optical fiber is indexed from the supply reel. A first tractor assembly including at least a first wheel receives optical fiber from the supply reel. A first length of optical fiber is clamped within the first wheel. A second tractor assembly including at least a second wheel receives a first length of optical fiber from the first tractor assembly. A second length of optical fiber is clamped within the second wheel. A load cell is reciprocally mounted to receive a first length of optical fiber from a second tractor assembly. Tension applied to the first length of optical fiber is increased. This tension is applied to the first length of optical fiber between the first wheel and the second wheel. This increasing tension is applied between an initial value and a predetermined maximum load.

After inspection, the first length of optical fiber is wound onto a take-up reel. a second wheel at a location where increasing tension is applied between the first wheel and the second wheel;
An optical fiber of length is indexed.

In other embodiments, the load cell is stationary and increasing tension is provided by rotating one or more capstans. In another embodiment of the invention, a conventional screener is replaced with a simple set of capstans.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a front view of an apparatus according to an embodiment of the invention is shown. The apparatus shown in FIG. 1 includes a frame 20. The apparatus shown in FIG. Extending outwardly from the frame 20 are two shafts (not shown) which are secured to opposite ends of the frame 20 and are connected to a supply reel.
The reel 12 and take-up reel 15 are supported. Also, frame 2
A first tractor assembly 24 and a second tractor assembly 25 are attached to the vehicle.

The first tractor assembly 24 includes a tractor wheel 21 rotatably mounted to the frame 20.
Equipped with: The tractor wheel 21 is rotated clockwise by a motor or other means, not shown. A belt 21a partially surrounds the tractor wheel 21 and extends upward therefrom, and has a triangular shape and connects three idler wheels 21b, 21c.
, and 21d. Belt 21a is held under tension by a spring (not shown) attached to the idler wheel. The bail 21a rotates clockwise as the tractor wheel 21 rotates. The tractor wheel 21 is arranged so that the optical fiber 11 can be contacted around it and clamped in place by the locking wheel 21 over the arc formed by the belt 21a.

The second tractor assembly 25 is also similar to the first. This includes the tractor wheel 22, belt wheels 22b, 22c, 22d, and belt 22a.
Equipped with: The tractor wheels 21 and 22 are
The optical fibers 11 rotate at the same speed so as to transport the optical fibers 11 along a path that is curved on the plane of their wheels.

The optical fiber 11 is introduced from the supply reel 12 to the joint between the belt 21a and the tractor wheel 21. Optical fiber 11 passes from supply reel 12 around idler wheel 16, dancer 13 and idler wheel 30 to first tractor assembly 24. Idler wheels 16 and 30 guide optical fiber 11. The idler wheel 30 is positioned to center the optical fiber 11 around the tractor wheel 21.

Especially when the rotational speeds of the supply reel 12 and the tractor wheel 21 are not synchronized, the dancer 13
In response to the speed of the tractor wheel 21, the optical fiber 11
Move up and down to adjust the slack.

The optical fiber 11 passes through the open space and around the grooved wheel 19 and grooved dancer 23 to the first tractor assembly 24. A grooved wheel 19 is secured to a frame 20, and a grooved dancer 23 is mounted for vertical movement on the frame 20. The optical fiber 11 forms a loop around the wheel 19 and dancer 23. Approximately 410
Gram weights (not shown) are suspended from the dancer 23 to maintain constant tension on the optical fiber 11. The constant tension applied to the optical fiber 11 by this weight is to suppress unnecessary sagging found in the indexed length of optical fiber. Optical fiber 11 passes from dancer 23 to tension stand assembly 40 .

Tension stand assembly 40 will be further described in connection with FIGS. 2 and 3. Tension stand assembly 40 includes a base 46 and a tension slide 43 attached to base 46. The load cell 41 is attached to a carrier bracket 47 so as to be movable back and forth along a tension slide 43. Tension slide 43 is a TOL-O-MATIC band cylinder (rodless cylinder) with a 11/4 inch bore. A piston is located within the tension slide and a steel bracket connects this piston to the carrier bracket 47. The tension slide 43 is equipped with two limit switches for regulating the stroke and resetting the regulation in the event of fiber breakage. Cushions at each end of the tension slide 43 provide smooth deceleration at the end of the full stroke. The cylinders are fed with filtered and lubricated air regulated to approximately 50 psi. The piston moves within the cylinder as it is pressurized.

The load cell 41 has a load mark on its face.
The pulley 4 is connected via two ball bearings (not shown) on the center post at a precise distance from the drive cell 41.
2 is installed. A rubber mount 45 is mounted to the bottom of the base 46 to aid vibration damping. As a safety measure in case the optical fiber 11 breaks, a safety shield 4 is installed on the base 46 after the tension slide 43.
4 is installed.

The pulley 42 connects the optical fiber 1 from the dancer 23.
Receive 1. Optical fiber 11 goes to second tractor assembly 25 and is clamped between belt 22a and tractor wheel 22 across the arc formed by belt 22a. Optical fiber 11 passes through the open space, around dancer 14, around idler wheel 17, and through second tractor assembly 25 to take-up reel 15. An idler wheel 17 guides the optical fiber 11. The dancer 14 moves up and down to remove the take-up reel 1 from the tractor assembly 25.
Adjust the slack of the optical fiber 11 up to 5.

Load cell 41 applies increasing tension to the clamped optical fiber at a location between the first and second tractor assemblies. The load cell 41 reciprocates along a tension slide to apply tension to the optical fiber 11 from an initial value to a predetermined maximum load. The load cell 41 is connected to the first tractor assembly 2
4 and the second tractor assembly 25 is subjected to approximately twice the load that the optical fiber 11 is subjected to. For example, a maximum load of 20 pounds on a load cell is
Each length of 1 is 10 pounds.

If the optical fiber 11 does not break when tension is applied from the load cell 41, a new length of optical fiber is indexed. The initial length of optical fiber is taken up on a take-up reel. The second length of optical fiber follows the path described above, is clamped by the first and second tractor assemblies, and is subjected to increasing tension from the load cell 41. After each application of tension, the optical fiber 11 is indexed from the supply reel 12 until the reel is empty.

The operation of the device will be understood from the above description of the device components shown in FIGS. 1, 2 and 3. A twenty meter length of optical fiber 11 is fed into tractor assembly 24, passed around load cell 41, and returned to tractor assembly 25. The optical fiber 11 is connected to the tractor wheel 21 and the belt 2.
The locking wheel 22 is located within the arc formed by the
is clamped in place by the With this mechanism, the belts 21a, 22a remain stationary when the optical fiber 11 is not moving. The lower portions of belts 21a, 22a apply relatively constant pressure to their tractor wheels and to the portion of optical fiber 11 between the belts and wheels. Conventional signal generation means may be used to detect the presence of optical fiber 11 at a location about load cell 41. When the presence of the optical fiber 11 is detected, the load cell 41 is activated and the tension slide 4 is activated.
Move backward along 3. During this rearward movement of the load cell, it can again be observed that the optical fiber 11 is clamped across the arc formed by the first and second tractor assemblies 24 and 25.

As the load cell 41 moves rearward, the display/recording device displays the load applied to the optical fiber 11. The tension in the fiber increases as the load cell moves rearward. When the load cell leaves its home position, the load is at some minimum value corresponding to the weight suspended from the dancer 23. As the load cell moves, the tension increases to a predetermined maximum value. In this manner, increasing tension is applied to the indexed length of optical fiber 11 in tractor assembly 24 and tractor assembly 25. At the end of the backward movement, the tension is released by returning the load cell 41 to its home position.

At this point in the sequence, the indexed length of optical fiber has been cycled and increasing tension has been applied. At the same time, wheels 21 and 2 are activated in response to signals from suitable conventional control means.
2 rotates freely and the optical fiber 11 is no longer clamped. This circulated length of optical fiber is wound onto a take-up reel and a new length of optical fiber 11 is indexed from supply reel 12.

Returning to FIG. 2, if optical fiber 11 breaks due to increasing tension applied by load cell 41, load cell 41 will move rearward along tension slide 43 to its farthest position. Continue. The actual failure load is maintained in memory and displayed on a display/recording device.

As previously mentioned, control of the various operations performed by the invention illustrated in FIG. 1 may be accomplished by conventional programming or sequencing means known to those skilled in the art to which the invention pertains. It can be realized.

The embodiment shown in FIG. 1 facilitates the insertion of optical fibers. The technology required is the conventional screen
It is similar to a durability testing device.

Other embodiments of the invention are shown in FIGS. 4-7. Identical parts are designated by the same reference numerals. The drawings do not indicate dimensions or relative distribution of the illustrated elements.

A first tractor assembly 24' and a second tractor assembly 25 attached to the frame 20
Refer to FIG. 4 for a detailed explanation of '. Braking means 26 are attached to the first and second tractor assemblies for clamping the optical fiber 11 during the fiber tensioning cycle. Brake means 26 hold tractor wheels 21' and 22' in place. The brake means 26 is connected to the tractor wheels 21' and 22.
Once applied, the belts 21a, 22a come to rest and crimp the fibers to the wheels 21', 22'.

FIG. 4 shows a modification of the tractor assembly in which weight 27 is connected to tractor assembly 24' and weight 28 is connected to tractor assembly 25'. The need to add weight is to increase the frictional force on the optical fiber. Otherwise, the optical fiber would be pulled through the friction lock consisting of the wheel and belt arrangement of the tractor assembly. If the optical fiber 11 were to slide over the tractor wheels 21' or 22', the surface of the fiber would wear and a significant loss in strength would occur.

FIG. 4 shows a modified example of the dancer 23', in which the weight 29 is used to maintain a constant tension on the optical fiber 11 when the optical fiber 11 is supplied from the supply reel 12. is connected to the dancer 23.

FIG. 5 shows another embodiment of the invention. In this embodiment, an optical fiber 55 is wound around a first capstan 54 and a second capstan 55 with constant tension, and the friction between the wound fiber and the surface of the capstan is clamped in place by the To maintain this friction, the supply lead
Tension is applied by the reel 52 and the take-up reel 51. A load cell 58 applies increasing tension to the optical fiber 55.

Similar to the load cell 41 shown in FIGS. 2 and 3, the load cell 58 reciprocates along a tension slide 57 to apply tension to the optical fiber from an initial value to a predetermined maximum load. 55. This embodiment of the invention has the advantage that little excessive force is applied to the optical fiber. The optical fiber is not crimped between two surfaces such that the surface of the fiber wears away resulting in significant loss of strength.

If optical fiber 55 does not break when tension is applied from load cell 58, a new length of optical fiber is indexed. The optical fiber 55 is a supply lead.
The reel 52 is indexed from its supply reel until it is empty. The optical fiber 55 is wound onto a take-up reel 51. A conventional controller 56 sends relay signals to the take-up reel, capstans 53 and 54 mounted on frame 50, and load cell 58 to initiate a new length of optical fiber 55.
is indexed, and the load cell 58 is moved along the tension slide 57.

Clamping in this embodiment and the embodiments shown in FIGS. 6 and 7 does not require additional surfaces for crimping against optical fiber 55 such as provided by belts 21a and 22a. .

Referring to FIGS. 6 and 7, capstan 63 is rotated in the direction of arrow 69 to increase the tension on optical fiber 65 to a predetermined load as shown on stationary load cell 66. let Optical fiber 65 is routed from supply reel 62 to first capstan 64.
and extends around the stationary load cell 66. Optical fiber 65 is clamped in place around capstan 64 by friction between the wrapped fiber and the surface of the capstan. supply lead to maintain friction against first capstan 64;
Tension is applied by the lever 62. Tension is applied by take-up reel 61 to maintain friction between the surface of capstan 63 and the wound fiber. Arrow 60 represents the direction of movement of optical fiber 65 from the load cell. An arrow 67 represents the direction of movement of the optical fiber 65 to the take-up reel 61. Take-up reel 61
is rotated at a speed to maintain the desired tension applied by the rotating capstan 63 and winding the excess portion of the optical fiber 65 when it is extended. In other embodiments, capstans 63 and 64
Incremental tension may be applied by simultaneous rotation of the two in the same direction.

EXAMPLE An example of an apparatus for measuring the actual load at break in an optical fiber will be explained with reference to FIG. A screener/rewinder 20 commercially available from Sterling Davis Electric, Wallingford, Conn., USA, was used. The screener 20 is
The take-up reel 15 goes around the pulley 42 from the pulley 12.
It was modified to automatically feed back 20 meters of optical fiber.

All physical loads were removed from the load cell. Sensotech, Co., Columbus, Ohio, USA
A signal conditioner, commercially available from Poration, was provided to convert the load cell electrical signal to digital form. Prior to dispensing, load cell 41 was checked to ensure that the indication provided by the signal conditioner was accurate.

A frame 46, a base plate, and a pneumatic slide 43 attached to the base plate.
A tension stand assembly 40 consisting of the following was provided. A commercially available roll from A.L. Design, Inc., Amherst, New York, USA.
A dock was set up. Pulley 42 was mounted on the face of load cell 41. Load cell 41 and pulley 42
is arranged to move along the tension slide 43. Load cell 41 was moved along tension slide 43 in the direction of screener 20, returning load cell 41 to its home position and beginning the tension cycle.

The gauge length counter in screener 20 was set to the desired length, 20 meters. scree
The total fiber length counter in na 20 was set to zero. A 24 kilometer reel is loaded onto the spindle and moved around the idler wheel 16, dancer 13 and idler wheel 30 to the first tractor assembly 24.
It was inserted into the screener 20 so as to enter the screen.

The screener speed is set to 20 percent of the maximum rotational speed of the tractor wheel 21 and turned on to allow the operator to manually thread the optical fiber 11 through other elements. The operator rotates the optical fiber.
Proceed to the screener 41, turn over the pulley 42, and remove the screener 2.
Returned to 0. Standing in front of the screener, the optical fiber 11
Approximately 6 feet of excess optical fiber 11 is supplied while maintaining tension at
turned off. Excess optical fiber 11 was threaded around second tractor assembly 25, under dancer 14, around the top of idler wheel 17, and secured to take-up reel 15. Optical fiber 11 was clamped within the arc of each tractor assembly formed by the tractor wheel and belt.

Once the 20 meters of optical fiber has been indexed and clamped in place, the load cell 41
increased its load from the initial value to 250 kpsi. Load cell 41 was moved from its home position to its maximum position for each indexed length of optical fiber. The screener stopped for one of three reasons: breakage, manual shutoff, and end of reel. Each break was recorded with an indication of the actual failure load and the total length of optical fiber delivered at the time of failure. In this example, the maximum level set corresponded to 250 kpsi. The graph of FIG. 8 shows the probability of failure (1=100%) at each intensity in kpsi for a 25 kilometer reel of optical fiber.

[Brief explanation of the drawing]

1 is a simplified front view of a first embodiment of the invention; FIG.

FIG. 2 is a front view of the tension stand assembly.

FIG. 3 is a side view of FIG. 2;

FIG. 4 shows another screen incorporated in another embodiment of the invention.
It's na.

FIG. 5 is a schematic diagram of another embodiment of the invention.

FIG. 6 is a schematic diagram of another embodiment of the invention.

7 is a schematic diagram of the capstan 63 shown in FIG. 6. FIG.

FIG. 8 is a graph characterizing the lower end of the intensity distribution for a 24 kilometer optical fiber.

[Explanation of symbols]

11: Optical fiber 12: Supply reel 13: Dancer 15: Take-up reel 16: Idler wheel 19: Grooved wheel 20: Frame 21: Tractor wheel 21a: Belt 21b, 21c, 21d : Idler wheel 22: Tractor wheel 22a: Belt 22b, 22c, 22d: Belt wheel 23: Grooved dancer 24: First tractor assembly 25: Second tractor assembly 30: Idler wheel 40: Tension Stand assembly 41: Load cell 43: Tension slide

Claims (7)

[Claims] [Claim 1] In an optical fiber strength testing method,
A) preparing a supply reel containing a predetermined length of optical fiber to be tested; B) supplying a predetermined length of said optical fiber such that the axis of the optical fiber is the axis of the first wheel. c) wrapping the optical fiber around at least a portion of the circumference of the second wheel in a perpendicular relationship to the optical fiber; D) wrapping the optical fiber around at least a portion of the circumference of the third wheel such that the axis of the optical fiber is orthogonal to the axis of the third wheel; E) suppressing movement of the optical fiber relative to at least the first wheel or the third wheel; and F) applying a continuously increasing tensile stress not exceeding a predetermined maximum stress to the optical fiber. the first and third wheels of the optical fiber;
G) if the optical fiber breaks, repeating steps (A) to (F); H) If the optical fiber does not break, relax the tensile stress in the optical fiber and run the wheels between the first and third wheels until a new length of optical fiber is extended between them. I) A method for testing the strength of an optical fiber, comprising repeating steps (E) and (F). 2. In the step (E), movement of the optical fiber is suppressed with respect to both the first wheel and the third wheel, and the tensile stress in the fiber is The second wheel is connected to the first wheel.
2. The method of claim 1, wherein said third wheel is generated by moving said wheel in a direction away from said third wheel. 3. The method of claim 1, wherein said variable is measured by a load cell associated with said second wheel. 4. Preventing rotation of the first wheel and the third wheel and clamping the optical fiber around the wheel in contact with the optical fiber. 4. The method of claim 3, wherein movement of said optical fiber is restrained relative to said first wheel and said third wheel. 5. Movement of the optical fiber relative to the wheels is inhibited by wrapping the optical fiber at least once around each of both wheels and preventing rotation of the wheels. 3. The method of claim 2. 6. The method of claim 5, wherein said variable is measured by a load cell associated with said second wheel. 7. The tensile stress is applied by: A) wrapping the optical fiber at least once around each of the first and third wheels; and B) wrapping the optical fiber around each of the first or third wheels. 2. The method of claim 1, wherein C) the rotation of one of the wheels is inhibited; and C) the other of the first or third wheels is rotated.